DESCRIPTION

Print
writes text to the standard output.
Fprint
writes to the named output
file descriptor;
a buffered form
is described in
bio(2).Sprint
places text
followed by the NUL character
(\0)
in consecutive bytes starting at
s;
it is the user’s responsibility to ensure that
enough storage is available.
Each function returns the number of bytes
transmitted (not including the NUL
in the case of
sprint),
or
a negative value if an output error was encountered.

Snprint
is like
sprint,
but will not place more than
len
bytes in
s.
Its result is always NUL-terminated and holds the maximal
number of complete UTF-8 characters that can fit.
Seprint
is like
snprint,
except that the end is indicated by a pointer
e
rather than a count and the return value points to the terminating NUL of the
resulting string.
Smprint
is like
sprint,
except that it prints into and returns a string of the required length, which is
allocated by
malloc(2).

The routines
runesprint,runesnprint,runeseprint,
and
runesmprint
are the same as
sprint,snprint,seprint
and
smprint
except that their output is rune strings instead of byte strings.

Finally, the routines
vfprint,vsnprint,vseprint,vsmprint,runevsnprint,runevseprint,
and
runevsmprint
are like their
v-less
relatives except they take as arguments a
va_list
parameter, so they can be called within a variadic function.
The Example section shows a representative usage.

Each of these functions
converts, formats, and prints its
trailing arguments
under control of a
format
string.
The
format
contains two types of objects:
plain characters, which are simply copied to the
output stream,
and conversion specifications,
each of which results in fetching of
zero or more
arguments.
The results are undefined if there are arguments of the
wrong type or too few
arguments for the format.
If the format is exhausted while
arguments remain, the excess
is ignored.

Each conversion specification has the following format:

% [flags] verb

The verb is a single character and each flag is a single character or a
(decimal) numeric string.
Up to two numeric strings may be used;
the first is called
width,
the second
precision.
A period can be used to separate them, and if the period is
present then
width
and
precision
are taken to be zero if missing, otherwise they are ‘omitted’.
Either or both of the numbers may be replaced with the character
*,
meaning that the actual number will be obtained from the argument list
as an integer.
The flags and numbers are arguments to
the
verb
described below.

The numeric verbs
d,o,b,x,
and
X
format their arguments in decimal,
octal, binary, hexadecimal, and upper case hexadecimal.
Each interprets the flags
0,h,hh,l,ll,u,+,-,,,
and
#
to mean pad with zeros,
short, byte, long, vlong, unsigned, always print a sign, left justified, commas every three digits,
and alternate format.
Also, a space character in the flag
position is like
+,
but prints a space instead of a plus sign for non-negative values.
If neither
short nor long is specified,
then the argument is an
int.
If unsigned is specified,
then the argument is interpreted as a
positive number and no sign is output.
If
precision
is not omitted, the number is padded on the left with zeros
until at least
precision
digits appear.
Then, if alternate format is specified,
for
o
conversion, the number is preceded by a
0
if it doesn’t already begin with one;
for
x
conversion, the number is preceded by
0x;
for
X
conversion, the number is preceded by
0X.
Finally, if
width
is not omitted, the number is padded on the left (or right, if
left justification is specified) with enough blanks to
make the field at least
width
characters long.

The floating point verbs
f,e,E,g,
and
G
take a
double
argument.
Each interprets the flags
+,-,
and
#
to mean
always print a sign,
left justified,
and
alternate format.
Width
is the minimum field width and,
if the converted value takes up less than
width
characters, it is padded on the left (or right, if ‘left justified’)
with spaces.
Precision
is the number of digits that are converted after the decimal place for
e,E,
and
f
conversions,
and
precision
is the maximum number of significant digits for
g
and
G
conversions.
The
f
verb produces output of the form
[-]digits[.digits].E
conversion appends an exponent
E[-]digits,
and
e
conversion appends an exponent
e[-]digits.
The
g
verb will output the argument in either
e
or
f
with the goal of producing the smallest output.
Also, trailing zeros are omitted from the fraction part of
the output, and a trailing decimal point appears only if it is followed
by a digit.
The
G
verb is similar, but uses
E
format instead of
e.
When alternate format is specified, the result will always contain a decimal point,
and for
g
and
G
conversions, trailing zeros are not removed.

The
s
verb copies a nul-terminated string
(pointer to
char)
to the output.
The number of characters copied
(n)
is the minimum
of the size of the string and
precision.
These
n
characters are justified within a field of
width
characters as described above.
If a
precision
is given, it is safe for the string not to be nul-terminated
as long as it is at least
precision
characters (not bytes!) long.
The
S
verb is similar, but it interprets its pointer as an array
of runes (see
utf(6));
the runes are converted to
UTF
before output.

The
c
verb copies a single
char
(promoted to
int)
justified within a field of
width
characters as described above.
The
C
verb is similar, but works on runes.

The
p
verb formats a single pointer or pointer-sized integer
(uintptr,
see
intro(2))
in hexadecimal.

The
r
verb takes no arguments; it copies the error string returned by a call to
errstr(2).

SOURCE

SEE

DIAGNOSTICS

Routines that write to a file descriptor or call
malloc
set
errstr.

BUGS

The formatting is close to that specified for ANSI
fprintf(2);
the main difference is that
b
is not in ANSI and
u
is a flag here instead of a verb.
Also, and distinctly not a bug,
print
and friends generate
UTF
rather than
ASCII.

There is no
runeprint,runefprint,
etc. because runes are byte-order dependent and should not be written directly to a file; use the
UTF output of
print
or
fprint
instead.
Also,
sprint
is deprecated for safety reasons; use
snprint,seprint,
or
smprint
instead.
Safety also precludes the existence of
runesprint.